1. Field of the Invention
The present invention relates to a plasma-addressing display device of a layer built structure which is formed by stacking display cells (e.g. liquid crystal cells) upon plasma cells, and more specifically to an electrode structure of the plasma cells for addressing on the basis of selective plasma discharge.
2. Description of the Related Art
As a means for realizing matrix-type liquid crystal display devices of higher resolution and higher contrast, an active matrix addressing technique has been conventionally known, in which switching elements such as thin film transistors are provided for display pixels (picture elements), respectively and the respective switching elements are driven in the order of lines (rows) of the matrix. In this prior art technique, however, since a great number of the semiconductor switching elements such as thin film transistors must be formed on a substrate, there exists a problem in that the production yield is deteriorated, in particular when a large area of the display device is required.
To overcome the above-mentioned problem, Buzak el al. have proposed a method of adopting plasma cells as addressing switch elements, in place of the thin film transistors, as disclosed in Japanese Published Unexamined (Kokai) Patent Application No. 1-217396, which corresponds to U.S. Pat. Nos. 4,896,149 and 5,077,553 and which are incorporated herein by reference.
The configuration of this prior art plasma-addressing display device for addressing display cells (e.g. liquid crystal cells) by means of plasma cells will be described briefly hereinbelow with reference to the attached drawing. As shown in FIG. 5, the display device is of a layer built structure such that a liquid crystal cell 101 is placed upon a plasma cell 102 via a dielectric partition (e.g. thin glass) 103. The plasma cell 102 is formed by a lower substrate 104 including a plurality of parallel arranged channels 105 formed on the surface thereof. The respective channels 105 are air-tightly sealed by the isolating barrier 103 and filled with an ionizable gas so as to form a plasma chamber 106 having separated spaces, respectively. In other words, the convex portions, 107 formed between the two adjacent channels 105 serve as side walls for separating the plasma chamber 106, respectively and additionally as gap spacers of the substrate 104 in cooperation with the isolating barrier 103. Further, a pair of parallel arranged electrodes 108 and 109 are provided on the bottoms of the channels 105, respectively. A pair of the electrodes are anode and cathode electrodes for ionizing the gas filled within the plasma chamber 106 to generate a discharge plasma.
The liquid crystal cell 101 is provided with a liquid crystal layer 111 sandwiched between the dielectric isolating barrier 103 and another transparent substrate 110. Further, signal electrodes 112 are formed on the inner surface of the transparent substrate 110. The signal electrodes 112 are formed by a transparent conductive thin film, and arranged so as to intersect the plasma chamber 106, respectively. Here, each signal electrode 112 is a column driving unit and each plasma chamber 106 is a row driving unit, respectively. Accordingly, pixels (picture elements) of the matrix arrangement are defined at the respective intersections of both the signal electrodes 112 and the plasma chamber 106. In the above-mentioned display device, the pixels are driven by scanning the plasma chamber 106 for generating a plasma discharge in the lines (rows) and further by applying analog driving voltages to the signal electrodes 112 arranged on the liquid crystal cell (101) side in synchronism with the line (row) order scanning. When a discharge plasma is generated within the plasma chamber 106, the potential of the whole chamber roughly reaches the anode potential. Under these conditions, when the driving voltages are applied to the pixels, electric charges are injected into the liquid crystal layer 111 at the respective pixels through the dielectric isolating barrier 103. Upon completion of the plasma discharge, the potential of the plasma chamber 106 changes to the stray potential, so that the injected electric charges are held at the respective pixels. In other words, since the so-called sampling holding operation can be implemented, the plasma chamber 106 functions as the sampling switches and the liquid crystal layer 111 functions as the sampling capacitances, so that the liquid crystal is activated according to the sampled electric charges to turn on or off the display device in each pixel unit.
In the above-mentioned prior art plasma-addressing display device, however, there exist various problems from the structural and manufacturing standpoints when the device is put into practice. In more detail, the grooves which constitute the plasma chamber have been generally formed on the basis of photolithographic and etching techniques. In practice, however, it is extremely difficult to form the highly precise, fine, dense grooves over a large area of the substrate, and therefore a considerable manufacturing cost is inevitably required. In, addition, the anode and cathode electrodes provided on the bottoms of a the respective grooves have been formed by means of selective etching technique, that is, by forming thin films in accordance with vacuum evaporating or sputtering procedures. Accordingly, a photomask for forming the plasma electrodes is required in addition to a photomask for forming the grooves. Further, it is extremely difficult to align both of the masks at a high precise positional relationship with respect to each other. Additionally, since the length of the thin film electrodes inevitably increases with increasing size of the display device, the resistance of the thin film electrode becomes relatively high and therefore the voltage applied to the electrodes drops along the electrode, thus resulting in another problem in that it is difficult to generate a stable plasma discharge over all of the display device.